This invention relates to a vibration damping material which is used for absorbing or isolating vibration, and particularly to a material for vibration-proof bed or base on which a precision working equipment or a precision measuring equipment is mounted for preventing external vibration or vibration arising from a power source incidental to the equipment from being transferred to a working unit or a measuring unit.
When machine tools such as NC lathes and grinding machines which are used for precision machining in micron or sub-micron order, precision working equipment like a photo repeater which is used for manufacturing semiconductor devices, and precision measuring equipment like a microscope are exposed to vibration, they are impeded in their intrinsic characteristics to bring ihto full play. Therefore, they are mounted usually on a bed having a function to absorb or isolate vibration.
The bed intended for such purpose has been constituted hitherto of steel, cast iron or rubber.
With a large rigidity, the bed constituted of steel or cast iron as above can hardly give rise to deformation like flexure when devices of large mass are installed thereon. However, such bed is not large in damping function of vibration and is insufficient in isolation characteristic of an infinitesimal vibration coming externally. Furthermore, such bed of iron group is so heavy itself that place of installation and transportation thereof are naturally restricted to inconvenience.
On the other hand, where the bed is constituted of an elastic material like rubber, a large vibration damping characteristic is obtainable, however, since rigidity is small, the bed is largely deformed itself, and thus is not suitable for having devices of large mass mounted thereon.
In view of the situation above, the inventors of this application proposed a vibration-proof bed formed with a new composite material at 1981 National Convention for Semiconductor Material Department, Institute of Electronics and Communication Engineers of Japan. The proposed new composite material used for the bed was obtained by making fine grains of iron oxide hardened with resin, and it was reported that a logarithmic decrement about 100 times superior to iron and aluminum was realized by means of the composite material containing ferrite particles of 0.05 to 0.1.mu. in size and polyester resin respectively at 90% by weight and 10% by weight. Further the composite material is lightweight to have a density one thirds or so of iron, and hence easy to transport and install. However, a mechanical strength of the composite material is 10.sup.6 N/m.sup.2 in order, which is inferior as compared with iron. Therefore its application was restricted more or less consequently.
An object of this invention is to provide a vibration damping material having a superior damping characteristic and an improved mechanical strength.
Another object of this invention is to provide a material for vibration-proof bed which is free from deviation in characteristic and high in practicability.